The on-going objectives of the immunotoxicology group are to select, refine and validate a panel of immune and host resistance procedures to better define immunotoxicity and correlate changes in immune function with altered host-resistance. We are completing the 2nd year of a two-year evaluation study examining a comprehensive panel of assays of which a number of these procedures have been selected for interlaboratory validation using suspect immunotoxic chemicals. This comprehensive assay panel examines: (1) host resistance to parasitic, bacterial, and tumor cell challenge; (2) cell-mediated immune functions; (3) natural killer (NK) cell activity; (4) bone marrow progenitor cell function; (5) humoral immune functions; and (6) macrophage function. We have examined selected chemicals of environmental concern as to their effect on the immune system and host resistance. Most of these chemicals are known human carcinogens and were examined to determine: (a) the carcinogenic-immunotoxic relationship; (b) structure-activity relationships; and/or (c) mechanisms of immunotoxicity. This approach should potentially allow for accurate assessment of human health risk as well as determining no-effect levels.